Physics 151 Week 3 Day 3 Topics Strategic Problem Solving Motion Diagrams & Motion Graphs with acceleration Adding and Subtracting Vectors Graphically

Strategic Problem Solving Strategy (PSS) On problems, it is important to show how you reasoned from the information given in the problem and key physics ideas to your final answer. The correct final answer with units is only worth 1-3 points. The remainder of the points are given for the quality of your solution.†You are expected to include the following to receive full credit: Prepare Identify the Physics: State explicitly which physics principle apply to the problem situation and that you will use to solve the problem Drawing a Picture: Draw at least one picture to visualize the physics of the problem and define your variables and constants. For motion problems this could be a motion diagram, motion graph, or pictorial diagram (Friday) Collecting Necessary Information: State all the information given in the problem with correct units. Include preliminary calculations such as unit conversions Solve Start with key equation(s) in symbol form Solve for the unknown quantity in symbols explicitly before numeric calculations Then substitute numbers with units and calculate the numeric answer Assess Check to see if your answer is reasonable Does it answer the question that was asked Does it have the right units? Be prepared to make reasonable estimations and state your assumptions when solving problems. Be aware of significant digits in your answers. (Keep lots of digits until the final calculation, then round to the appropriate precision. For intermediate steps, remember to keep one extra siginificant digit Answer: B Slide 1-7

Question Velocity vectors point in the same direction as displacement vectors. in the opposite direction as displacement vectors. perpendicular to displacement vectors. in the same direction as acceleration vectors. Velocity is not represented by a vector. Answer: A Slide 1-8

Answer Velocity vectors point in the same direction as displacement vectors. Answer: A Slide 1-9

Vectors Slide 3-9

Adding Vectors Graphically Slide 1-33

Vector Subtraction Slide 3-10

Find the following resultants graphically Adding Vectors Find the following resultants graphically Answer: B Slide 1-7

Checking Understanding Which of the vectors below best represents the vector sum P + Q?   Answer: A Slide 3-13

Answer Which of the vectors below best represents the vector sum P + Q?   Answer: A Slide 3-14

Checking Understanding Which of the vectors below best represents the difference P – Q?   Answer: B Slide 3-15

Answer Which of the vectors below best represents the difference P – Q?   Answer: B Slide 3-16

Acceleration Vectors Slide 3-11

The diagram below shows two successive positions of a particle; it’s a segment of a full motion diagram. Which of the acceleration vectors best represents the acceleration between vi and vf?   Answer: D Slide 3-28

Answer The diagram below shows two successive positions of a particle; it’s a segment of a full motion diagram. Which of the acceleration vectors best represents the acceleration between vi and vf?   Answer: D Slide 3-29

From the Knight Workbook, Chapter 2, Problem 16A The motion diagram on the rights shows an initial point 0 and a final point 1. A pictorial model would define five symbols, x0 and x1 (or y0 and y1), v0 and v1, and a. Determine whether each of these quantities is positive, negative, or zero. place either +, --, or 0 in each cell of the table below. Clicker Choices A. + B. -- C. 0 Answer: C Slide 2-4

Ball on Ramps (From an Exam) A ball is released from rest at the point shown on the incline and speeds up. It then rolls onto a level section of track at constant speed, and then rolls onto a second incline with the same slope as the first where it slows down. The diagram below shows the location of the ball at several instants in time. NOTE: THIS IS NOT A STROBE PHOTOGRAPH OR MOTION DIAGRAM. Draw a motion diagram for the ball’s mostion from t = 0.6 s to 5.1 s Draw delta v diagrams for each motion interval Use the delta v diagrams to find the ball’s acceleration Answer: B

Example: Velocity Vectors Jake throws a ball at a 60° angle, measured from the horizontal. The ball is caught by Jim. Draw a motion diagram of the ball with velocity vectors. Slide 1-35

Motion Graph Demonstrations Answer: C Slide 2-4